ACK/Cmnt: [SRU][J/I/H/F][PATCH 0/1] Drop "UBUNTU: SAUCE: cachefiles: Page leaking in cachefiles_read_backing_file while vmscan is active"

[Tim Gardner]

Acked-by: Tim Gardner <tim.gardner at canonical.com>

Looks good assuming the reproducer results also look good. I assume 
Bionic will be a separate patch ?

On 10/19/21 4:33 AM, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1947709
> 
> [Impact]
> 
> "UBUNTU: SAUCE: cachefiles: Page leaking in cachefiles_read_backing_file while
> vmscan is active" has been applied to fix a page leaking issue.
> 
> However a slightly different fix has been applied upstream:
> 
>   9a24ce5b66f9 ("cachefiles: Fix page leak in cachefiles_read_backing_file while vmscan is active")
> 
> Basically we are fixing the same issue in two different ways at the same time,
> but even worse our patch an introduce a potential NULL pointer dereference: we
> do a put_page(newpage) and set newpage = NULL in the main for() loop and then
> we may do additional put_page(newpage) after the main for loop if
> ret == -EEXIST, that would trigger the NULL pointer dereference.
> 
> [Test case]
> 
> No test case or reproducer is available at the moment, this issue has been
> found simply by reviewing the code.
> 
> [Fix]
> 
> Drop the SAUCE patch and rely on the upstream fix.
> 
> [Regression potential]
> 
> If the analysis is not correct we may re-introduce a page leak in cachefiles
> (NFS for example), but it seems unlikely to happen, since the upstream fix is
> addressing the page leaking already.
> 
> 

-- 
-----------
Tim Gardner
Canonical, Inc